Many women see an obstetrician/gynecologist (OB/GYN) annually and receive their primary care from an OB/GYN. Understanding OB/GYNs' human papillomavirus (HPV) vaccination practices, including knowledge of and barriers to vaccination, is essential to design effective interventions to increase vaccination. This study evaluated OB/GYN knowledge, attitudes, and beliefs regarding vaccinating both younger (18-26 years) and mid-adult (27-45 years) women. Data were collected from OB/GYN providers in October 2019 through a nationwide web-based survey. Items included the following: HPV-related vaccination practices, recommendation strength, knowledge (seven items), benefits (four items), and barriers (eight items). The sample (n = 224) was majority were White (69%), men (56%), and practice in suburban clinics (55%). Most (84%) reported they usually or always recommend HPV vaccine to eligible patients, but estimated only about half (51%) of other OB/GYNs did the same. Recommendation strength varied by patient age with 84% strongly recommending it to patients ≤18 years, compared with 79% and 25% strongly recommending to younger and mid-adult patients, respectively (p < 0.01). Participants reported lower benefits (p = 0.007) and higher barriers (p < 0.001) for 27- to 45-year-old patients compared with younger patients. Cost was the most frequently reported barrier, regardless of patient age. Overall knowledge was high (m = 5.2/7) but 33% of participants did not know the vaccine was safe while breastfeeding. Although providers reported strongly and consistently recommending the HPV vaccination to their adult patients, there were gaps in knowledge and attitudinal barriers that need to be addressed. Provider performance feedback may be important in improving HPV vaccination awareness among providers.